Dean Koga and Michael Schuller gave an interesting and useful talk on the protection of original Tiffany stained glass windows at the Congregation Shearith Israel in New York City during heavy renovation work there. The talk gave a clear outline of what they did and how others can prepare for such events. It should be noted that there was little warning between the time that the Congregation was informed of the work and the start of the work.
They carried out the following actions (which I would strongly recommend):
- Look for local engineering expertise in vibrations and the monitoring of vibrations. Michael Schuller represented this company.
- Look at existing (inter)national standards for the protection of buildings due to vibrations including those caused by construction work. These included building codes for New York City, international codes for France and Russia, and the vibration literature.
- Document fully any preexisting damage in the stained glass windows
- Look at the levels of current existing vibrations due to, for example, traffic, wind, opening and closing of the windows or doors. This showed that such events, as well as the opening and closing of the windows themselves were also a source of background vibration and shock.
- Determine limits for vibrations including a warning limit, and a limit where work has to immediately stop. These were 0.15 in/sec (3.75 mm/s) and 0.2 in/s (5 mm/s) for the low vibration frequencies expected.
- Negotiate with contractors to use more “gentle” construction methods. The contractors agreed to avoid using a wrecking ball for razing the old part of the synagogue, and to use augured piles for the foundation instead of pile driving.
The precautions were successful. No damage was found after demolition work, and only one new crack was found near an operable window. It was interesting to hear that wind pressure on the windows actually increased due to exterior protection. The authors were aware that the vibration sensor they used, a geophone actually designed for earthquake monitoring, was too heavy for the job, but time constraints limited their choices. A lightweight (several grams) sensor placed on the window frame or horizontal supports would have been better.
The authors recommended more studies on systems to protect stained glass windows, and testing to determine how much deformation/displacement such windows can tolerate. I would certainly agree with that.